The mainframe is a large-scale computer system used as, for example, a business-critical system for companies and the like. Hardware and software which are used for the mainframe are often designed to be dedicated to that mainframe, so that the mainframe is highly reliable and has high throughput; however, the mainframe has the disadvantage of requiring considerable maintenance cost.
On the other hand, an open system is a computer apparatus constructed by combining general-purpose hardware and software; and although the operation system is inferior to the mainframe in terms of the reliability and the throughput, it has the advantage that it can be introduced and operated inexpensively. Therefore, in recent years, an increasing number of companies have been replacing their computer used in the business system from the mainframe to the open system for the purpose of cost reduction.
Such computer replacement work requires migration of an operation executed on the mainframe to the open system. Then, such operation migration work from the mainframe to the open system is performed by changing all programs for executing the operation to a format according to the open system, porting them to the open system, and then suspending the operation on the mainframe side once, and subsequently resuming the operation on the open system side.